Yep, like that, though dip molds are usually one piece. So is the type of mold I'm talking about, if by dip mold you mean something that was used to give an initial shape to a parison which was then further worked.
Seems like with cast on bosses you'd be able to see the juncture. There's no evidence that the bosses were cut anywhere (except on one of the Hawkes vases that has decoration engraved on the bosses, first photo). I've noticed that they all seem to have sort of a border, a impression a few mm wide encircling the bosses, which I believe was created by the mold. It's not obvious enough to be a part of the cut pattern.
I keep coming back to the optical properties of the bosses. If the glass is not indented on the inside and the were cut to shape on the outside, you wouldn't see the distortion caused by the non-uniformity of the glass. Compare the ones we've been looking at with the vase in the second photo, which has cut bosses (and I think is Sinclaire, not Hawkes). The ones on the sides that are refracting the image of the cut design show how little distortion there is. The third photo demostrates pretty well, I think, that the bosses are thicker than the rest of the glass.